The present invention relates to a new and improved power steering control valve, and more specifically, to a power steering control valve which is hydraulically balanced and has a mechanically balanced force transmitting assembly which resists relative rotation between inner and outer valve members.
A power steering control valve having a force transmitting assembly which resists relative rotation between inner and outer valve members with a force which varies as a function of vehicle speed is disclosed in U.S. Pat. No. 4,819,545, issued Apr. 11, 1989 and entitled "Power Steering System". The power steering control valve disclosed in this patent includes an upper reaction element which presses a plurality (four) balls against a reaction surface formed as part of a one piece outer valve member. The upper reaction element is held against rotation relative to the inner valve member by a pair of force transmitting elements or balls. Thus, the power steering control valve illustrated in the aforementioned U.S. patent requires six force transmitting elements or balls which engage accurately located recesses in the inner valve member, the upper reaction element, and the outer valve member.
During operation of a power steering control valve, such as the power steering control valve disclosed in the aforementioned U.S. patent, it is desirable to have the valve hydraulically balanced so that equal fluid pressures are conducted to a power steering actuator in response to equal clockwise and counterclockwise actuation of the valve members relative to each other from an initial position. It is also desirable to have the force with which the force transmitting assembly resists relative rotation between the inner and outer valve members be equal for equal displacements clockwise and counterclockwise of one of the valve members relative to the other valve member.
The obtaining of both hydraulic pressure and mechanical force balancing of the power steering valve disclosed in the aforementioned U.S. patent requires that the components of the valve be accurately made. If a slight inaccuracy occurs in the making of the inner and outer valve members or the reaction element so that the initial position of the inner and outer valve members relative to each other has to be adjusted slightly from an intended initial position, it is impossible to adjust the position of the force transmitting assembly relative to the inner and outer valve members to obtain a mechanical balance at the adjusted initial position. This is because the relationship between the components of the force transmitting assembly cannot be adjusted relative to the valve members.